Mold insert for use in a mold for the manufacture of a cushioning element for sports apparel

ABSTRACT

An aspect of the present invention relates to a mold insert for use in a mold for the manufacture of a cushioning element for sports apparel. Further aspects of the present invention relate to a mold using such a mold insert, a method for the manufacture of a cushioning element for sports apparel using such a mold, and a cushioning element manufactured by such a method.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to and claims priority benefits from GermanPatent Application No. 102019215838.2, filed on Oct. 15, 2019 (“the '838application”), and European Patent Application No. 20200125.1, filed onOct. 5, 2020 (the '125 application”). Both applications are herebyincorporated herein in their entirety by this reference.

FIELD OF THE INVENTION

The present invention relates to a mold insert for use in a mold for themanufacture of a cushioning element for sports apparel, particularly forthe manufacture of a shoe sole or a midsole, wherein the cushioningelement is manufactured from particles of an expanded material, andwherein an electromagnetic field is used as an energy carrier to fusethe particle surfaces. The present invention also relates to a moldusing such a mold insert.

The present invention further relates to a method of structuring such amold insert using optimization methods, and to a method of manufacturinga mold insert structured in this manner.

In addition, the present invention relates to a method for themanufacture of a cushioning element for sports apparel, particularly ashoe sole or a midsole, from particles of an expanded material, whereinan electromagnetic field is used as an energy carrier to fuse theparticle surfaces, and wherein the method uses such a mold. The presentinvention further relates to a cushioning element, particularly a shoesole or a midsole, manufactured by such a method.

BACKGROUND

Over the recent years, the use of particle foam materials, i.e.,materials made from individual particles of expanded plastic materials,has found its way into the manufacture of cushioning elements for sportsapparel, particularly the manufacture of shoe soles for sports shoes. Inparticular, the use of particles of expanded thermoplastic polyurethane(eTPU), which are fused at their surfaces by subjecting them topressurized steam within a mold (often called “steam chest molding” inthe art), has been considered for the manufacture of shoe soles. In thiscontext, the use of particles from eTPU has turned out to be desirablebecause their use can result in shoe soles with low weight, goodtemperature stability and small hysteresis-losses with regard to theenergy exerted for the deformation of the sole during running, i.e., agood energy return to the wearer of the shoe.

However, to obtain dimensionally stable components of a high quality,the heat energy must also be provided to the interior of the componentin order to obtain a sufficient degree of fusion between the particles.For heat energy supplied by steam (or, even worse, when a liquid bindermaterial is used, which has also been considered), this is only possibleup to a certain thickness and packing density of the particles in themold and, beyond a certain ‘threshold’ thickness or density, steam-chestmolding will generally lead to imperfections, particularly in theinterior of the component.

Another disadvantage of using steam as an energy carrier is that a majorshare of the energy stored within the steam may be lost heating the moldinstead of being supplied to the particle surfaces. This can, on the onehand, necessitate a long preheating phase until the mold (often madefrom metal materials) is heated up to a saturation temperature, and can,on the other hand, delay stabilization and cooling of the fusedcomponent since the mold may have stored a large amount of heat energythat delays cooling. Moreover, as conventional molds are usually largein their dimensions, this results in a slow heating of the mold and asignificant associated energy consumption. Therefore, the method may beprotracted and very energy inefficient.

To address these drawbacks, energy carriers other than pressurized steamhave therefore been considered. In particular, a method for themanufacture of a cushioning element for sports apparel that comprisesloading a mold with a first material comprising particles of an expandedmaterial and fusing the surfaces of the particles by supplying energy inthe form of at least one electromagnetic field has been described in DE10 2015 202 013 A1 and EP 3 053 732 A1.

However, the methods disclosed in these two applications still leaveroom for improvement because they do not yet take full account of thecomplex geometry of the parts that, in particular, modern performancefootwear like running shoes often include, specifically when it comes totheir soles and midsoles. The complex geometry of these parts, in turn,puts very high demands on the manufacturing equipment and manufacturingmethods. For the case of using particle foam materials in the soles andmidsoles, this means having to ensure that also for sole geometries withnoticeable variations in thickness, curvature, contouring, etc., an evenand stable connection between the particle surfaces must be ensured inall areas of the sole and throughout the interior of the sole. With theknown methods and machinery, this may be difficult or in some cases evenimpossible to achieve.

Based on the described prior art, it is therefore a problem of thepresent invention to provide improved tools and methods for themanufacture of cushioning elements for sports apparel from particles ofexpanded materials and using an electromagnetic field as an energycarrier, which allow the production of high-quality products withcomplex geometry. Another problem that is addressed by the presentinvention is the provision of improved methods to make such tools.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed description, embodiments of the invention aredescribed referring to the following figures:

FIG. 1: Illustration of the technical complications arising for themanufacture of cushioning elements having complex geometrical featuresfrom particles of expanded material using an electromagnetic field as anenergy carrier for the fusion of the particle surfaces;

FIG. 2: Embodiments of inventive mold inserts;

FIG. 3: Permittivity of materials suitable for use in inventive moldinserts; and

FIG. 4: Dielectric loss factor of the materials of FIG. 3.

SUMMARY

The terms “invention,” “the invention,” “this invention” and “thepresent invention” used in this patent are intended to refer broadly toall of the subject matter of this patent and the patent claims below.Statements containing these terms should be understood not to limit thesubject matter described herein or to limit the meaning or scope of thepatent claims below. Embodiments of the invention covered by this patentare defined by the claims below, not this summary. This summary is ahigh-level overview of various embodiments of the invention andintroduces some of the concepts that are further described in theDetailed Description section below. This summary is not intended toidentify key or essential features of the claimed subject matter, nor isit intended to be used in isolation to determine the scope of theclaimed subject matter. The subject matter should be understood byreference to appropriate portions of the entire specification of thispatent, any or all drawings and each claim.

In some aspects, the present disclosure is directed to a mold insert foruse in a mold for the manufacture of a cushioning element for sportsapparel, a. wherein the cushioning element is manufactured fromparticles of an expanded material, b. wherein an electromagnetic fieldis used as an energy carrier to fuse the particle surfaces, c. whereinthe mold insert has been manufactured using an additive manufacturingmethod, and d. wherein the mold insert is adapted to locally adjust thefield strength of the electromagnetic field inside a molding cavity ofthe mold, based at least in part on the geometry of the cushioningelement. The mold insert may be adapted to increase the homogeneity ofthe field strength throughout molding cavity during the manufacture ofthe cushioning element. The local adjustment of the field strengthinside the molding cavity may be at least partially caused by a localvariation in the dielectric properties of the mold insert. The localadjustment of the field strength inside the molding cavity may be atleast partially caused by a local variation in the permittivity of themold insert. The local variation in the permittivity of the mold insertmay be at least partially caused by a local variation in the density ofthe material of the mold insert. In some aspects, a higher density ofthe material of the mold insert results in a higher permittivity of themold insert. The local density of the material of the mold insert maylie between 0.4 g/cm³ and 1.7 g/cm³. The local adjustment of the fieldstrength inside the molding cavity may be at least partially caused by alocal variation in the dielectric loss factor of the mold insert. Thelocal dielectric loss factor of the mold insert may lie between 0.01 and0.10, in particular between 0.01 and 0.07. The mold insert may bearranged adjacent to the molding cavity and influences the geometry ofthe molding cavity. The mold insert may be arranged adjacent to themolding cavity and influences the geometry of the molding cavity and thelocal variation in the dielectric loss factor may further influence theamount of surface heat-up of the surface of the mold insert which isadjacent to the molding cavity during the manufacture of the cushioningelement. In some aspects, the cushioning element is a sole for a shoe,in particular a midsole.

In some aspects, the present disclosure is directed to a mold for themanufacture of a cushioning element for sports apparel from particles ofan expanded material, a. wherein an electromagnetic field is used as anenergy carrier to fuse the particle surfaces, and b. wherein the moldcomprises a mold insert according to the above paragraph.

In some aspects, the present disclosure is directed to a method for themanufacture of a cushioning element for sports apparel from particles ofan expanded material, a. wherein an electromagnetic field is used as anenergy carrier to fuse the particle surfaces, and b. wherein the methoduses a mold according to the above paragraph.

In some aspects, the present disclosure is directed a cushioning elementmanufactured with the method according to the above paragraph. In someaspects, the cushioning element is a sole. In some aspects, thecushioning element is a midsole.

BRIEF DESCRIPTION

The above-outlined problem is addressed and is at least partly solved bythe different aspects of the present invention.

A first aspect of the present invention relates to a mold insert. In anembodiment, a mold insert for use in a mold for the manufacture of acushioning element for sports apparel is provided, particularly for themanufacture of a shoe sole or a midsole, wherein the cushioning elementis manufactured from particles of an expanded material, and wherein anelectromagnetic field is used as an energy carrier to fuse the particlesurfaces. The mold insert has been manufactured using an additivemanufacturing method, and the mold insert is adapted to locally adjustthe field strength of the electromagnetic field inside a molding cavityof the mold, based at least in part on the geometry of the cushioningelement.

One advantage of using an electromagnetic field (in the followingsometimes simply called “the field”, for conciseness), in particular,electromagnetic radiation, as an energy carrier in the fusion ofparticles of expanded material compared to using steam is that theprovision of energy by the electromagnetic field is not coupled to thetransport of mass. An electromagnetic field can therefore (under certainconditions, e.g., that the mold is not entirely or predominately madefrom metal or another electroconductive material) permeate the interiorof the component that is being molded more easily and, thus, lead to aneven and consistent fusion of the particles throughout the component.Generally speaking, the electromagnetic field leads to a dielectricheating of the particles and the particle surfaces, which then fusetogether to form the molded component.

For components with a ‘regular’ geometry, like simple plates of materialwith a constant thickness throughout and using only one kind ofmaterial, e.g. particles of expanded material, the surfaces of thematerial such as the surfaces of all of the particles will heat up quiteuniformly, leading to an even and consistent fusion throughout theplate.

However, for components such as cushioning elements with complicatedgeometry, for example, the shoe soles often encountered in modernperformance footwear, the situation becomes more involved. Due to thecomplex geometry of the cushioning element, the molding cavity in whichit is manufactured will have regions with varying thickness, curvature,contouring, etc., too. This will in general distort the electromagneticfield permeating the mold and the molding cavity and lead to someregions with increased field strength, while other regions may suffer a‘dilution’ i.e. a reduced field strength of the electromagnetic field.Since the energy density in the electromagnetic field is ω ∝ {rightarrow over (E)}·{right arrow over (D)} (leaving out the magneticcontribution, and where {right arrow over (E)} is the electric field and{right arrow over (D)} is the electric displacement field), this meansthat more energy is provided to the particles in the regions ofincreased field strength, compared to the regions of reduced fieldstrength. This can lead to an uneven and inhomogeneous fusion of theparticle surfaces and, eventually, to a flawed and unacceptable finalproduct.

To address this problem, the inventive mold insert is shaped in such amanner that it compensates, at least partially, for this effect. Inprinciple, two options are possible in this regard:

First, the mold insert may be placed into the mold in such a manner thatit locally adjusts the field strength inside the molding cavity withoutinfluencing the geometry of the molding cavity. The insert may, forexample, be ‘sandwiched’ between other parts of the mold.

Second, the mold insert may not only locally adjust the field strengthinside the molding cavity, it may also itself define at least part ofthe molding cavity. For example, the mold insert may be arrangeddirectly adjacent to the molding cavity and form part of the wall of themolding cavity (or it may at least define the geometry of part of themolding cavity but be further coated or covered by additional layers ofmaterial, for example).

In any case, there is an interplay between the mold insert and thegeometry of the component, such as the above-mentioned cushioningelement, that is being manufactured. The interplay is such that the moldinsert takes account of the geometry of the cushioning element (andhence the geometry of the molding cavity), and the mold insert adjuststhe electromagnetic field specifically for that geometry and as neededto obtain the desired fusion of the expanded particles. This is what ismeant by adjusting the electromagnetic field “based at least in part onthe geometry of the cushioning element”. Of course, other factors havegenerally to be taken into account, too, like the geometry and materialof the rest of the mold and/or the kind of electromagnetic field that isused. Therefore, the adjustment will only be based “in part” on thegeometry of the cushioning element. Still, the mold insert is tailoredfor the specific geometry of a given cushioning element, and differentinventive mold inserts will generally be used for different componentgeometries.

A further factor that must be considered in this regard is the kind ofparticles that are used. While the mold insert may initially be designedto adjust the electromagnetic field in the empty molding cavity in thedesired manner (for example, as a first-order approximation in thedesign of the mold insert), the ultimate goal is to adjust the field asdesired in the filled state of the mold, because it is in this statethat the electromagnetic field will pass its energy to the particlesurfaces for their fusion (and generally also to their bulk volume).Since the particles themselves have certain dielectric properties—whichgenerally change for different base compounds from which the particlesmay be made, for example—these properties should desirably be taken intoaccount in the design of the mold insert, so that the electromagneticfield has the desired distribution throughout the filled molding cavityduring the actual fusion process.

The particles of expanded material for the cushioning element maycomprise at least one of the following materials: expanded thermoplasticpolyurethane (eTPU), expanded polyamide (ePA), expandedpolyether-block-amide (ePEBA); expanded polylactide (ePLA); expandedpolyethylene terephthalate (ePET); expanded polybutylene terephthalate(ePBT); expanded thermoplastic polyester ether elastomer (eTPEE).

For example, for use in the manufacture of shoe soles, particles ofeTPU, ePEBA and/or ePA have turned out to be desirable and may hence beused in the context of the present invention.

To allow the desired adjustment, creating the mold insert with anadditive manufacturing process is particularly suitable. Additivemanufacturing processes allow for a fine-tuned control not only of thegeneral geometry of the mold insert, but also its interior, which canplay an important role in providing the desired ‘distortion’ to theelectromagnetic field. Moreover, modern additive manufacturing processesallow the production of parts in a very short timeframe and on-site,such that the product development process is not stopped (at least notfor very long) by having to wait for the manufacture orre-manufacture/adaption of the manufacturing tools, which conventionallyoften delay the process by days or even weeks.

Designing the mold insert for additive manufacture can involve one orseveral options and methods, wherein combinations are, of course, alsopossible. The simplest case would be a simple trial-and-error approach,which may be feasible due to the short time it takes from providing thedesign of the mold insert until the finished mold insert is produced,due to the fact that additive manufacturing is used. A second approachis to use computer simulations of the distribution of theelectromagnetic field (e.g. the local field strength) through the moldand, in particular, the mold insert and molding cavity.

One possibility for designing the mold insert may use a desired targetdistribution of the electric displacement field {right arrow over (D)}in the (filled) molding cavity as a starting point. As is known fromstandard electrodynamics, on a macroscopic level and inside a dielectricmaterial the electric displacement field {right arrow over (D)}describes the combined effect of an externally applied electric fieldand the polarization effects induced inside the dielectric material bythe external field, and in this sense represents the “effective field”inside the material. The electric displacement field D is thereforesuitable quantity to consider for specifying a design target for themold insert in the context of the present invention. However, other“target functions” (e.g., a desired distribution of the electric field{right arrow over (E)} are also possible.

As further described below, the local adjustment of the field strengthinside the molding cavity can e.g. be caused (at least in part) by alocal variation in the (relative) permittivity of the mold insert, whichcan in turn be influenced by a local variation in the density of thematerial of the mold insert. In addition, the material or materialmixture used in different parts and regions of the mold insert can alsoinfluence the permittivity of the mold insert, and hence the fielddistribution inside the molding cavity.

As also further described in detail below, the mold insert is made usingadditive manufacturing methods (e.g., 3d-printing- or depositiontechniques), which generally involve controlling both the fill- orfeeding rate with which material is supplied to the “printing head” ofthe additive manufacturing device, as well as the composition of thematerial used for the additive build-up process of the mold insert.

An optimization process for designing the mold insert may therefore bebased on the fill- or feeding rate as well as the material compositionor “mixing rule” as input parameters, and the above-described targetfunction, e.g., the desired electric displacement field {right arrowover (D)} in the (filled) molding cavity, as a design goal. To performthe optimization, the (as yet unknown) structure or shape of the moldinsert may, for example, be discretized into a lattice of cells orpixels, and at each lattice site the local density of the mold insert asa function of the fill rate and mixing rule may be varied and optimized,by using the dielectric heating equation to compute the fielddistribution inside the molding cavity that results from a givendistribution of local densities over the lattice sites (further physicalparameters besides the local density may be involved in the optimizationprocess, too). By varying the density distribution over the lattice, theeffect on the resulting field distribution inside the molding cavity maybe investigated, and an optimal configuration may thus be chosen ordetermined (e.g., by minimizing an “energy function”). Since the localdensity is, in turn, specified as a function of the fill rate and mixingrule, the density distribution obtained as a result of the optimizationprocess can eventually be translated into a set of parameters andinstructions that allow the manufacture of an optimized mold insert orstructure by using additive manufacturing methods.

In any case, once the design has been created on a computer, forexample, it may be manufactured quickly and then verified by test runson an actual machine, and subsequently further tuned or altered, ifnecessary. Due to the use of additive manufacturing processes, it may bepossible that the entire process from the first design to an acceptabletool may be done on a short timeframe of a few weeks or even days.

The mold insert can, in particular, be adapted to increase thehomogeneity of the field strength throughout the molding cavity duringthe manufacture of the cushioning element.

Since the energy density in the electromagnetic field is ω ∝ {rightarrow over (E)}·{right arrow over (D)} (again leaving out the magneticcontribution), a homogeneous field strength will facilitate an evenfusion of the particles throughout the cushioning element, such thathomogenizing the field is particularly suitable to obtain cushioningelements with consistent and even fusion of the particle surfacesthroughout.

On the other hand, by reversing the argument, it is also clear that themold insert may be used to create specific regions in the fielddistribution (e.g., the local value of the field strength) where anincreased or reduced amount of fusion will take place (assuming the sameparticles are used everywhere; otherwise the varying composition of theparticles will also have an effect on the amount of fusion). This may bedesirable to provide different regions of the cushioning elements withdifferent performance properties like stiffness, for example.

The local adjustment of the field strength inside the molding cavity canat least partially be caused by a local variation in the dielectricproperties of the mold insert.

Of course, a variation of the dielectric properties of the mold insertwill, first of all, generally alter the field inside the mold insertitself. However, contrary to the idealized case of an infinitelydimensioned plate condenser into which a plate of dielectric material isinserted and where the field outside the dielectric material is leftunaltered due to the formation of ‘just the right amount’ ofpolarization charges at the surface of the plate of dielectric material,in the case of a finite-dimension mold insert with a generally complexgeometry there will also be an effect on the electromagnetic fieldoutside the mold insert itself and, in particular, within the moldingcavity. In particular, this is true if the mold insert is arrangeddirectly adjacent to, or even forms part of, the wall of the moldingcavity. The mold insert may in this sense be considered a ‘dielectriclens’ for the electromagnetic field which changes its distributionthroughout the molding cavity.

The local adjustment of the field strength inside the molding cavitycan, in particular, be at least partially caused by a local variation inthe permittivity of the mold insert.

The permittivity of the mold insert has a direct influence on the fieldstrength inside the mold insert (for a constant ‘external’ field beingapplied to the mold), as the skilled person understands, and due to theeffects mentioned above, will also influence the field distribution(e.g., the local value of the field strength) inside the molding cavity.A further advantage of using the permittivity as a ‘control knob’ toinfluence the field distribution is that materials with a wide varietyof permittivity-values are known and available, such that a large degreeof tuning and adaption is possible in this manner by choosing and/orcombining different materials in the additive manufacturing process.

The local variation in the permittivity of the mold insert may be atleast partially caused by a local variation in the density of thematerial of the mold insert.

Apart from using different materials with different intrinsicpermittivity-values, another advantage of using the permittivity toadjust the field is that the same material, but with differentdensities, may be used in different regions of the mold insert to obtainthe desired influence. The density may be a ‘strictly localized’ densitymeasured in as small a region of the mold insert as this is technicallypossible, e.g., the density of a sample cube with edges of 1 mm length,or it may be an ‘averaged’ density measured on a large distance scale,e.g., an average value of the density determined from a sample cube withedges of 5 mm length, or 10 mm length, for example. Since additivemanufacturing is used to produce the mold insert, such densityvariations are furthermore relatively easily achievable, such that thecombination of these two aspects is particularly desirable.

For example, one way to obtain such a local variation in the density ofthe material of the mold insert is by the inclusion of air cavitieswithin the material. The ability to create complex distributions of aircavities is a particular advantage of using additive manufacturing forthe mold insert. The inclusion of such air cavities is hence oneimportant option provided by the present invention to locally tune thematerial density and therefore the permittivity, and hence the fielddistribution within the molding cavity.

Generally, a higher density of the material of the mold insert resultsin a higher permittivity of the mold insert.

The local density of the material of the mold insert may lie between 0.4g/cm³ and 1.7 g/cm³.

For the materials discussed in more detail below that may be used forthe additive manufacture of an inventive mold insert, such values are onthe one hand technically achievable without too many difficulties, andon the other hand result in mold inserts that strike a desirablecompromise, for example, between heat-up of the mold itself and thedegree of influence on the field inside the molding cavity. If thedensity is too low, the mold insert will generally not heat upsufficiently, which will be detrimental to the fusion, and, if thedensity is too high, the mold insert will heat up too much and hence,for example, unnecessarily prolong the fusion and subsequentcooling/curing process.

Suitable values for the local permittivity may lie between 1 and 20, forexample.

Alternatively, or in addition, the local adjustment of the fieldstrength inside the molding cavity can at least partially be caused by alocal variation in the dielectric loss factor of the mold insert.

Contrary to the case of a variation in the permittivity, a localvariation in the dielectric loss factor of the mold insert may not (oronly to a more limited degree) have a direct influence on the fielddistribution, in particular outside the mold insert and within themolding cavity. However, a local variation in the dielectric loss factorof the mold insert may lead to different degrees of energy absorptionand hence heating of the different regions of the mold insert. Since thepermittivity is generally a function of temperature, these differentdegrees of heating of the different regions of the mold inserts cancause a local variation in the permittivity which can then cause a localadjustment of the field, also outside the mold insert and, inparticular, within the molding cavity.

On the other hand, the local variation in the dielectric loss factor ofthe mold insert can also have a more direct influence the fusion of theparticle surfaces, by virtue of the different degrees of heating, andhence the different degrees of energy emitted into the molding cavity inthe form of heat radiation, for example. This influence will generallybe the more pronounced the closer the mold insert is arranged to themolding cavity, and it will generally also have a larger effect for thefusion of the particles arranged at the surface of the cushioningelement and facing the mold insert than for particles arranged in theinterior or at a different side of the cushioning element. This processmay therefore intentionally be used, for example, to provide specificproperties to a surface layer of a region of the cushioning element. Forexample, the particles in a surface layer of the cushioning element maybe more strongly melted in a region adjacent to a part of the moldinsert where it has a high dielectric loss factor and hence emits alarge degree of heat into the direction of the molding cavity. Such morestrongly melted particles may, after cooling, provide increasedstiffness to the respective region of the cushioning element, forexample.

Also, while too much energy loss caused by unwanted heating of the moldis generally to be avoided, some degree of heating of the mold and, inparticular, the mold insert, may be desirable. This pre-heating may beused to pre-heat the particles of the expanded material prior to theiractual fusion which may broaden the processing window and generallyfacilitate the fusion process.

For example, the local dielectric loss factor of the mold insert can liebetween 0.01 and 0.10, in particular between 0.01 and 0.07.

This range has proven to be suitable because it provides a goodcompromise between the level of energy absorption of the mold insert andenough heating of the mold insert to facilitate fusion, i.e. not toomuch energy being absorbed by the mold insert on the one hand, but alsoenough heating of the mold insert to facilitate the fusion of theparticle surfaces as described above on the other hand.

Other values are also possible, however which may be up to 0.3. Forexample, using polyvinylidene fluoride (PVDF), also calledpolyvinylidene difluoride, in the construction of the mold insert,values of 0.2 or even higher can also be realized. This may allow for aparticularly “noticeable” amendment to the field distribution insections or positions of the molding cavity where this is necessary ordeemed desirable, for example.

As already mentioned, the mold insert may be arranged adjacent to themolding cavity and thus influence the geometry of the molding cavity.Specifically, in this case, the local variation in the dielectric lossfactor can then also influence the amount of surface heat-up of thesurface of the mold insert which is adjacent to the molding cavityduring the manufacture of the cushioning element.

The mold insert can hence play a double, or even triple role, in that itnot only influences the distribution of the electromagnetic field, butalso serves to (partly) define the geometry of the cushioning elementand may even influence the temperature inside the molding cavity, whichis an important parameter in the fusion process.

The additive manufacturing method for the mold insert can comprises atleast one of the following methods: 3d printing; a micro-melt-drop basedmethod; a powder-bed based method; stereolithography, SLA; selectivelaser sintering, SLS; selective laser melting, SLM; continuous liquidinterface production, CLIP; fused deposition modeling, FDM; digitallight processing, DLP; multi jet modeling, MJM; a polyjet method; a filmtransfer imaging method, FTI; electron beam melting, EBM; electron beamadditive manufacturing, EBAM; subtractive rapid prototyping, SRP.

At least one of the following materials may be used for the mold insert:a ceramic filled resin; a cyanate ester; a polylactic acid/polylactide,PLA; an acrylonitrile butadiene styrene, ABS; polyamide 6/nylon 6, PA6;polyamide 66/nylon 66, PA66; polyamide 12/nylon 12, PA12; a polyetherether ketone, PEEK; a binder system; an epoxy resin; a UV-curingthermoset.

Combinations of different methods and/or different materials are alsopossible.

The electromagnetic field can provide the energy to fuse the particlesurfaces in form of electromagnetic waves in the radiofrequency part ofthe spectrum of 30 kHz-300 MHz, or in the microwave part of the spectrumof 300 MHz-300 GHz, in particular, in the form of electromagnetic waveswith a frequency in the range of 25-30 MHz.

The use of these kinds of radiation are desirable for a number ofreasons. First, both radiofrequency- and microwave generators arecommercially available and may be implemented into a manufacturing toolwith comparatively little effort. In addition, it may be possible tofocus the radiofrequency- or microwave radiation generally onto themolding cavity such that the energy efficiency of the method isincreased. Furthermore, the intensity and frequency of theradiofrequency- or microwave radiation may easily be changed and adaptedto the respective requirements. Particularly, the use of radiation witha frequency in the range of 25-30 MHz has turned out to be desirable inthe context of the present invention. In combination with theabove-described materials and mechanisms regarding the inventive moldinsert, this frequency range allows a good control of the fielddistribution inside the molding cavity.

The cushioning element can, in particular, be a sole for a shoe, moreparticularly a midsole.

As mentioned, shoes sole and, in particular, midsoles nowadays oftenhave quite a complicated geometry. The use of an inventive mold insertin the production of such elements brings the advantages of the presentinvention to particular fruition.

A further aspect of the present invention relates to a mold. In anembodiment, a mold for the manufacture of a cushioning element forsports apparel from particles of an expanded material is provided,wherein an electromagnetic field is used as an energy carrier to fusethe particle surfaces. The mold comprises embodiments of an inventivemold insert.

It goes without saying that all of the features, feature-combinations,options and possibilities described in this application with regard tothe mold insert may be applied to the case of a full molding tool, too,and also in the manufacturing method described herein.

In an embodiment, the mold comprises at least two mold parts, and eachof the two mold parts comprises an electrode that is used in theprovision of the electromagnetic field. The mold insert is placed intoone of the two mold parts, and the two mold parts may be moved relativeto one another in a first direction to open the mold in order to allowloading the mold with the particles, and the two mold parts can furtherbe moved relative to one another in a second direction to close the moldin order to form the molding cavity between the electrodes.

Such a setup allows for an easy exchange of the mold insert and thegeneral operation of the mold. In particular, in the case that the moldinsert at least partially also defines the geometry of the moldingcavity, the same overall tool may be used with different mold insertsfor the production of a number of different cushioning elements.

It is also possible that a mold insert is used that completely surroundsthe molding cavity, for example a mold insert with a first part (e.g. atop part) and a second part (e.g., a bottom part) which are placed intothe two mold parts (e.g., using a mold with an upper mold part and alower mold part).

It is also mentioned, however, that the tool may itself be tailoredtowards the manufacture of a specific type or class of cushioningelement, for example, a specific type of midsole. In particular, thegeometry of one or both of the electrodes may be such that the generatedelectromagnetic field is already basically tuned for the manufacture ofthe midsole (or some different kind of cushioning element), and that aninventive mold insert is then used to further adjust the electromagneticfield on a finer level, e.g., to take account of different shoe sizes,different overpronation-/underpronation-protection-characteristicsdesirable for the sole, different additional sole elements like torsionbars that may or may not be included in the sole, and so forth.

For example, the above-mentioned two mold parts or at least a portion ofthem may comprise capacitor plates as electrodes, which may be arrangedon an inner side of the mold parts (i.e. on the side of the parts facingthe molding cavity). These mold parts may be comprised of a layeredconstruction such as a base plate, a molding plate defining at leastpart of the molding cavity and an insulating layer on the inside of themolding plate (i.e. the side facing the cavity). The capacitor platesmay also be included in such layered constructions. In some embodiments,other layered constructions are used.

In an embodiment, the thickness of the molding plates and/or thecapacitor plates is varied. For example, by varying the thickness of themolding plates and/or the capacitor plates, the mold parts may becontoured. This allows fine tuning of the energy that is to be appliedto the midsole (or some different kind of cushioning element orcomponent) in the tooling mold. In some embodiments, the capacitorplates may be adjusted as it might allow to keep the same molding plateswhich may be more economical than adjusting the molding platesthemselves.

Of course, adaptability to such factors may also be achieved solely (butmaybe to a smaller degree) by using an inventive mold insert, togetherwith two ‘standard’ electrodes that are not specifically geared towardsa particular product or product class. In this sense, the use ofinventive mold inserts can also help to enlarge the field ofapplicability of a standard molding tool or mold assembly.

Another aspect of the present invention is provided by method for makingan inventive mold insert using an additive manufacturing process. Themethod may include an optimization process of the structure of the moldinsert as described above, wherein a target function is specified andthe mold structure is optimized to meet the specifications provided bythe target function. In particular, the optimization process may employthe fill rate as well as the material composition or mixing rule of thematerial used for the additive manufacturing process of the mold insertas input parameters, and the desired electric displacement field in the(filled) molding cavity as a design goal. To perform the optimization,the (as yet unknown) structure or shape of the mold insert maybediscretized into a lattice of cells or pixels, and at each lattice sitethe local density of the mold insert as a function of the fill rate andmixing rule may be varied and optimized, by using the dielectric heatingequation to compute the field distribution inside the molding cavitythat results from a given distribution of local densities over thelattice sites. The optimized local density distribution may then betranslated into a set of parameters and/or instructions that are used byan additive manufacturing machine to create the mold insert using thedetermined fill rate and mixing rule.

An example implementation for the above-mentioned optimization processof the structure of the mold insert will be explained in detail in thefollowing:

An additive manufactured version of a tooling mold for the dielectricheating process may be constructed. Within this tooling mold, a complex3D-shape of an additive manufactured structure of the mold insertcontaining multiple different heights, widths and material densities maybe shaped to form the molding cavity. Within this molding cavity, acomponent made from an expanded thermoplastic elastomer (eTPE), such asparticles from expanded thermoplastic polyurethane (eTPU) for theabove-mentioned cushioning element, may be manufactured. The additivemanufactured tooling mold itself may comprise conductive aluminumelectrodes, e.g. anode and cathode, and a dielectric mold insertmaterial surrounding the material of the component.

Initially, the dielectric mold insert may be printed with a materialfill rate of 100%, i.e. the dielectric mold insert may be formed out ofa full density of the selected dielectric mold insert material. Forexample, a polylactic acid/polylactide, PLA; an acrylonitrile butadienestyrene, ABS; polyamide 6/nylon 6, PA6; polyamide 66/nylon 66, PA66;polyamide 12/nylon 12, PA12; a polyether ether ketone, PEEK; apolyethylene terephthalate, PET; a PE material; apolytetrafluorethylene, PTFE; a binder system; an epoxy resin; aUV-curing thermoset may be used.

Upon inspection of the performance of this tooling mold construction byusing a Finite Element Method (FEM) simulation approach supplied withother relevant process parameters (such as the frequency of a suppliedA/C voltage generated by an electromagnetic field generator and avoltage value applied between the anode and the cathode electrodes), theelectric field strength occurring within the dielectric mold insertmaterial and within the material of the component may be computed basedon the Maxwell's equations. This initial computation may reveal anuneven distribution of the electric field strength, whereby the electricfield strength within the component may appear highest in areas of lowermaterial densities of the component's material and may correspondinglyappear lower in areas of high material density.

To average out the observed differences in the occurring electric fieldstrength, the optimization process according to the present applicationmay be used to design the topology of the additive manufactureddielectric mold insert. Here, a volumetric integral function may becalculated for the normalized electric field distribution across thecomponent within the molding cavity. This value may be denoted byE_(av). For each point in the corresponding normalized fielddistribution, the following objective function Phi, φ, may be applied:

$\phi = {\left( {E_{pp} - E_{av}} \right)^{2}\left\lbrack \frac{kg^{2}*m^{2}}{s^{6}A^{2}} \right\rbrack}$

where E_(pp) may be the computed electric field strength density foreach infinitesimally small point in the molding cavity. In order tooptimize for the occurring material density within the dielectric moldinsert, a topology optimization density model may be applied to all suchvolumetric regions of the mold insert geometry. A domain controlvariable may be discretized on nodes or elements and a fictitiousmaterial may be introduced to account for the material boundary in animplicit way. An interpolation may be then constructed such that thephysical governing equation may be solved wherever the control variablemay be equal to one, while an equation associated with the fictitiousmaterial may be solved where the control variable may be equal to zero.The interpolation may be specific to the physics and may be constructedsuch that intermediate value of the control variable may be suboptimal.

By applying the Lichtenecker's equation for the bulk materialpermittivity of the target optimization domain by the followingequation:

${\ln \mspace{11mu} ɛ_{*}} = {\sum\limits_{i}^{n}{v_{i}*\ln \mspace{14mu} ɛ_{i}}}$

where v_(i) is the volume fraction of the i^(th) constituent, ε_(i) isthe permittivity of the i^(th) constituent, n is the number of totalconstituents in the component's material and the total volume fractionin the equation is given by Σ_(i) ^(n)v_(i)=1, the mold insert materialmodel used for the Finite Element Method simulation may be modifiedduring optimization iterations to yield a change in the dielectricpermittivity value of the mold insert material. According to the outputdensity model value (0<B, <1) of the above-mentioned optimizationprocess, the simulation model may yield an integral solution for thedielectric field strength for each iteration of the optimization cycle.

The termination of the optimization approach may happen either byconverging to a set optimality tolerance for the solution, or byreaching a set maximum number of model evaluations. The end result ofthe above-mentioned optimization process may be a density map across thedielectric mold insert material, yielding a value for theabove-mentioned topology optimization density model variable θ_(c) foreach point across the volume integration of the dielectric mold insertmaterial, which in turn may create a local modification of the sourcematerial model properties based on the relationship denoted by theabove-mentioned Lichtenecker's equation for the bulk materialpermittivity of the target optimization domain.

The success of the optimization process may be evaluated by thecomputation of the dielectric field strength across the molding cavityfor the component using the modified material permittivity of thematerial matrix gained as an output of the density model of theabove-mentioned optimization process, and comparing this field strengthto the original objective function Phi φ.

The skilled person will understand that this example implementation isonly one way for the optimization process according of the presentapplication and other methods, algorithms or approaches may also beapplied.

Yet another aspect of the present invention relates to a manufacturingmethod for a cushioning element for sports apparel, particularly a shoesole or a midsole. In an embodiment, a method for the manufacture of acushioning element for sports apparel from particles of an expandedmaterial is provided, wherein an electromagnetic field is used as anenergy carrier to fuse the particle surfaces, and wherein the methoduses embodiments of the inventive mold.

Further aspects of the present invention relate to a cushioning element,in particular, a sole or a midsole, manufactured with embodiments of theinventive manufacturing method as well as a shoe, in particular, asports shoe, comprising such a sole or a midsole.

As already explained above, by using an inventive mold insert, it ispossible to manufacture cushioning elements with complex geometry whichstill have the desired fusion and connection between the particlesthroughout, because the mold insert allows to adjust and adapt thedistribution of the electromagnetic field (e.g., the local fieldstrength) within the molding cavity and during the molding process insuch a manner that the desired degree of fusion is achieved locally in acontrolled manner. This can provide a significant advantage over knownmethods not using such a mold insert, where such a local control may bedifficult or even impossible.

DETAILED DESCRIPTION

Possible embodiments of the different aspects of the present inventionare described in the following detailed description primarily withrespect to tools and methods for the manufacture of shoe soles. It isemphasized, however, that the present invention is not limited to theseembodiments. Rather, it may also be used for different kinds ofcushioning elements for sports equipment, sports footwear and sportsapparel, like for example knee- or elbow protectors.

Reference is further made to the fact that in the following onlyindividual embodiments of the invention may be described in more detail.The skilled person will understand, however, that the optional featuresand possible modifications described with reference to these specificembodiments may also be further modified and/or combined with oneanother in a different manner or in different sub-combinations, withoutdeparting from the scope of the present invention. Individual featuresmay also be omitted, if they are dispensable to obtain the desiredresult. In order to avoid redundancies, reference is therefore made tothe explanations in the preceding sections, which also apply to thefollowing detailed description.

FIG. 1 schematically illustrates the technical complications that canarise when an electromagnetic field is used as an energy carrier to fuseparticles of expanded material at their surfaces in the manufacture acushioning element with complex geometrical features.

On the top left of FIG. 1, generally indicated by reference 100, asketch is shown of the manufacture of a simple plate 110 of materialwith constant thickness in a mold 120 using an electromagnetic field(indicated by the arrows 130) as an energy carrier to fuse the surfacesof a plurality of particles 140 of an expanded material. Due to theconstant thickness of the plate 110 and its simple geometry, theelectromagnetic field is essentially homogeneous throughout the tool, asindicated by the constant thickness of the arrows 130, and the fusion ofthe surfaces of the particles 140 caused by their dielectric heating bythe electromagnetic field will therefore generally also be even andconsistent.

On the top right of FIG. 1, by contrast, generally indicated byreference 150, the manufacture of a component 160 also from particles140 of an expanded material but now with a more complex geometry issketched, here for the case of a component 160 having differentthicknesses in different regions 161, 162 and 163. Due to this complexgeometry and the resulting shape of the molding cavity of the tool usedfor the manufacture, the strength of the electromagnetic field used forthe fusion of the particles 140 is no longer constant throughout butchanges between the different regions 161, 162 and 162, as indicated bythe different thicknesses of the arrows 131, 132 and 133 representingthe field in these different regions. As a result, while an even andconsistent fusion of the surfaces of the particles 140 may still beachieved in one region, e.g., in the middle region 162 (s. the particlefoam component generally indicated by reference 172), in the remainingregions 161 and 163 the surfaces of the particles 140 may either showonly a low degree of fusion or may even be insufficiently fused (s. theparticle foam component generally indicated by reference 171), or theymay show too high a degree of fusion and be over-fused or even burnt (s.the particle foam component generally indicated by reference 173).

To address this problem of a potentially inhomogeneous and uneven fusionof the particle surfaces for cushioning elements with complex geometry,the present invention provides an additively manufactured mold insertthat serves to at least partially compensate for such effects, byadjusting the electromagnetic field permeating the molding cavity.

FIG. 2 sketches embodiments 210, 220 and 230 of inventive mold inserts.In all three embodiments, the mold insert is depicted as completelyenclosing the molding cavity (it is noted, though, that only atwo-dimensional cut through the three-dimensional mold insert is shownin each case, which cannot capture all details of the three-dimensionalshape of the respective mold insert). It is noted that generally themold inserts 210, 220, 230 will be separable into at least two parts,for example a top part and a bottom part, such that the molding cavitymay be loaded with the particles and the fused component be removed fromthe mold. Such separation lines between the different parts of the moldinsert are not shown in FIG. 2, however, for simplicity.

It is further mentioned that an inventive mold insert may e.g. also beprovided as an insert for only an upper part or a lower part of a moldin which it is used (more details on such a mold follow below), andhence only be bordering the molding cavity on one side. As alreadymentioned, an inventive mold insert may even be incorporated into a moldat a position where it is not directly adjacent to the molding cavity atall, but influences the field distribution within the molding cavitynonetheless. Even though these possibilities are not further discussedin much detail below, they also form part of the present invention.

The mold insert 210 only comprises one type of material. However, eventhough the entire mold insert 210 is made of the same material, becausethe material of the mold insert 210 has different thicknesses indifferent regions, the material can still ‘distort’ the permeatingelectromagnetic field in the desired manner. In addition, a localvariation in the density may be used to further enhance this effect, forexample.

The mold insert 220 builds on the general construction of the moldinsert 210, but now different materials are used in different regions ofthe mold insert 220. The different materials are called “Material A”,“Material B” and “Material C” in FIG. 2. In addition to using suchdifferent materials, the dielectric properties (e.g., permittivity,dielectric loss factor) may also be changed locally within one of thegiven material regions. The “Material A”, “Material B” and “Material C”may, for example, be chosen from the materials discussed in the presentdocument, in particular from the materials discussed in the context ofFIGS. 3 and 4, potentially with the further constraint that thedielectric loss factor shall be larger than 0.01 (more details on thiswill follow below).

Finally, the mold insert 230 builds further on the general constructionof the mold insert 220, where now three different material structures(made from the same material or from different materials, e.g. from thethree different materials “Material A”, “Material B” and “Material C” ofthe mold insert 220) are employed in the different regions. Thedifferent material structures are called “Structure A”, “Structure B”and “Structure C” in FIG. 2. Here, the additive manufacturing of theinventive mold inserts comes desirably to fruition, since such methodsallow for the creation of complicated and ‘open’ (i.e., includingcavities, channels, etc.) inner structures, which may otherwise not beachievable. Such inner structures can, in particular, help to change thelocal density and/or the local dielectric properties of the differentregions or sections of the mold insert 230, and hence the way the moldinsert influence the permeating electromagnetic field. As one possibleexample, the three different structures may comprise air cavities of adifferent (average) size, resulting in a different (average) density ofthe mold insert 230 in the respective regions, and hence differentpermittivity-values.

Instead of three different regions or sections, the mold inserts 220 and230 may also comprise a different number of regions or sections, e.g., 2or 4 or 5. The number of different regions or sections may also differbetween the top- and the bottom part of the insert (for an insert havingboth a top and bottom part). Also, the materials used in the top- andthe bottom part need not necessarily correspond or be the same, but canalso be different, at least partially.

As mentioned, the mold inserts 210, 220 and 230 may be used in a mold(not shown) for the manufacture of a cushioning element for sportsapparel, for example, for the manufacture of a midsole for a sports shoe(e.g., a running shoe), from particles of an expanded material, whereinan electromagnetic field is used as an energy carrier to fuse theparticle surfaces.

Particles that may be used in the context of the present invention are,in particular, particles of expanded thermoplastic polyurethane (eTPU),expanded polyether-block-amide (ePEBA) and/or expanded polyamide (ePA),as well as mixtures therefrom. These materials have turned out to bedesirable for the manufacture of shoe soles, e.g. because of their goodenergy return and their temperature independence.

Additionally, or alternatively, the particles may also comprise or becomprised of at least one of the following materials: expandedpolylactide (ePLA), expanded polyethylene terephthalate (ePET), expandedpolybutylene terephthalate (ePBT), expanded thermoplastic polyesterether elastomer (eTPEE), or mixtures thereof.

The mold may comprises an upper mold part and a lower mold part, whichcooperate to define a molding cavity in which the cushioning element(e.g. a shoe sole) is molded.

One possibility is that the mold insert completely surrounds the moldingcavity (s., e.g., the mold inserts 210, 220 and 230) and hence definesthe geometry of the molding cavity. In this case, a bottom part of themold insert may be placed into the lower mold part, and a top part ofthe mold insert may be placed into the upper mold part.

Another possibility is that the lower mold part comprises a ‘die’ ornegative which cooperates with an inventive mold insert which is placedinto the upper mold part and acts as a ‘plunger’ or positive, to formthe molding cavity when the mold is closed (or the other way around).

For completeness, it is once again mentioned that an inventive moldinsert can generally also be arranged at another position within themold, e.g., be arranged as a layer or sub-layer of the upper or lowerpart of the mold, without directly influencing the geometry of themolding cavity but still serving to influence and adjust the way inwhich the electromagnetic field permeates the molding cavity.

Instead of an upper mold part and a lower mold part, a medial andlateral mold part may also be used, for example, or more than two moldparts may be employed. Analogous statements also apply for the moldinserts covered by the present invention.

Returning, for the sake of definiteness, to the case of a mold having anupper mold part and a lower mold part, each of the two mold parts maycomprises an electrode used for the provision of the electromagneticfield. In the simplest case, the electrodes may simply be condenserplates or metal plates with simple geometry. In other embodiments,however, the electrodes may also have a shape generally corresponding tothe cushioning element that is to be manufactured in the mold, to‘pre-shape’ the electromagnetic field for the fusion of the cushioningelement. Further ‘fine-tuning’ of the electromagnetic field can then beachieved by means of an inventive mold insert.

The electromagnetic field generated between the electrodes may providethe energy to fuse the particle surfaces in form of electromagneticwaves in the radiofrequency part of the spectrum of 30 kHz-300 MHz, orin the microwave part of the spectrum of 300 MHz-300 GHz. In aparticular embodiment, it provides the energy to fuse the particlesurfaces in the form of electromagnetic waves with a frequency in therange of 25-30 MHz.

The two (or more) mold parts may be able to move relative to one anotherin a first direction (e.g., vertically away from each other) to open themold and in order to allow loading the mold with the particles, and themold parts may further be able to move relative to one another in asecond direction (e.g., vertically towards each other) to close the moldin order to form the molding cavity between the electrodes.

During loading, the mold may be completely opened, and the two moldparts be entirely separated from one another, or the mold may only beopened partially and to a certain extent, such that the two mold partsstill ‘engage’ with one another to a certain degree and limit theloading volume available for loading the particles into. This ‘crack-gaploading’ option can serve to influence the physical properties of themanufactured cushioning element already during loading, e.g., itsdensity and stiffness, by controlling the amount of particles that areincorporated into cushioning element and/or the degree of compressionthe particles experience upon complete closing of the mold. This mayalso allow manufacturing different kinds of cushioning element with thesame mold, by adjusting the crack-gap height (i.e., the extent to whichthe mold is opened) during loading.

Returning to the discussion of the inventive mold inserts covered by thepresent invention, like e.g. the mold inserts 210, 220 and 230, a numberof different additive manufacturing methods and a number of differentbase materials may be used for their manufacture.

For example, the additive manufacturing method may comprise at least oneof the following methods and processes: 3d printing; a micro-melt-dropbased method; a powder-bed based method; stereolithography, SLA;selective laser sintering, SLS; selective laser melting, SLM; continuousliquid interface production, CLIP; fused deposition modeling, FDM;digital light processing, DLP; multi jet modeling, MJM; a polyjetmethod; a film transfer imaging method, FTI; electron beam melting, EBM;electron beam additive manufacturing, EBAM; subtractive rapidprototyping, SRP.

Moreover, the mold insert may comprises at least one of the followingmaterials: a ceramic filled resin; a cyanate ester; a polylacticacid/polylactide, PLA; an acrylonitrile butadiene styrene, ABS;polyamide 6/nylon 6, PA6; polyamide 66/nylon 66, PA66; polyamide12/nylon 12, PA12; a polyether ether ketone, PEEK; a binder system; anepoxy resin; a UV-curing thermoset.

Using such methods and materials, the inventive mold inserts may beadapted to locally adjust the field strength of the electromagneticfield inside the molding cavity of the mold, based at least in part onthe geometry of the cushioning element. An inventive mold insert may, inparticular, be manufactured and provided in this manner which increasesthe homogeneity of the field strength throughout molding cavity duringthe manufacture of the cushioning element.

As discussed above, for cushioning elements with a complex geometry, thematerial distribution with the tool and/or the shape of theelectromagnetic field generated by the tool may be such that theelectromagnetic field permeating the molding cavity is distorted in sucha manner that ‘cool spots’ and ‘hot spots’ are created during the fusionof the particles of expanded material via the energy carried andsupplied by the electromagnetic field. This can lead to an uneven andpotentially even unacceptable end result of the fusion process. The moldinsert serves to compensate for and at least partially level out sucheffects, in order to improve the quality of the production result.

As already mentioned, the local adjustment of the field strength insidethe molding cavity can at least partially be caused by a local variationin the dielectric properties of the mold insert.

Of course, other factors like the frequency or intensity distribution ofthe generated electromagnetic field will generally also influence thedistribution of the field inside the molding cavity, as the skilledperson understands. But changing the dielectric properties of the moldinsert provides a particular handle to tune the field distribution(e.g., the local field strength) inside the molding cavity, which doesnot require a significant alteration in the general setup andconstruction of the molding tool, which may be particularly desirable,for example, for prototyping, but also in general as every setup changein the basic machinery may be very time- and cost-consuming.

One specific way to adjust or at least influence the field strengthinside the molding cavity is by a local variation in the permittivity ofthe material of the mold insert.

Values for the (relative) permittivity of materials suitable for use inan inventive mold insert, measured at 27.12 MHz, are shown in FIG. 3:

-   -   Curve 310 shows the permittivity of a material called PerFORM        with a density of 1.61 g/cm³ over the temperature range from 20°        C.-120° C. PerFORM is a ceramic composite stereolithography        material.    -   Curve 320 shows the permittivity of a PET material with a        density of 1.39 g/cm³ over the temperature range from 20°        C.-120° C.    -   Curve 330 shows the permittivity of a PLA (polylactide acid)        material with a density of 1.24 g/cm³ over the temperature range        from 20° C.-120° C.    -   Curve 340 shows the permittivity of CE 221, which is a cyanate        ester resin, with a density of 1.21 g/cm³ over the temperature        range from 20° C.-90° C.    -   Curve 350 shows the permittivity of a PE material with a density        of 0.93 g/cm³ over the temperature range from 20° C.-120° C.

With the exception of the PE material, all investigated materialsexhibit an increase in permittivity with increasing temperature. Also,for the shown materials, permittivity correlates with the density of thematerials, i.e., a higher density means a higher permittivity.Alternatively, or additionally, to using different materials (e.g., thematerials discussed in the context of FIG. 3), the local variation inthe permittivity of an inventive mold insert can therefore, at leastpartially, be caused by a local variation in the density of the materialof the mold insert. Typically (at the very least for the materials shownin FIG. 3), a higher density of the material of the mold insert resultsin a higher permittivity of the mold insert. Suitable values for thelocal density of the material of an inventive mold insert lie between0.4 g/cm³ and 1.7 g/cm³.

Or, in terms of suitable values for the permittivity, values between 1and 20 have generally turned out to be desirable to obtain the desiredinfluence on the field distribution within the molding cavity.

Another way to locally adjust or at least influence the fielddistribution (e.g. the local field strength) inside the molding cavityis by a local variation in the dielectric loss factor of the moldinsert.

Values for the dielectric loss factor of materials generally suitablefor use in an inventive mold insert, measured at 27.12 MHz, are shown inFIG. 4 (the materials are the same materials as discussed in the contextof FIG. 3 above):

-   -   Curve 410 shows the dielectric loss factor of the PerFORM        material with the density of 1.61 g/cm³ over the temperature        range from 20° C.-120° C.    -   Curve 420 shows the dielectric loss factor of the PET material        with the density of 1.39 g/cm³ over the temperature range from        20° C.-120° C.    -   Curve 430 shows the dielectric loss factor of the PLA material        with the density of 1.24 g/cm³ over the temperature range from        20° C.-120° C.    -   Curve 440 shows the dielectric loss factor the CE 221 with the        density of 1.21 g/cm³ over the temperature range from 20° C.-90°        C.    -   Curve 450 shows the dielectric loss factor of the PE material        with the density of 0.93 g/cm³ over the temperature range from        20° C.-120° C.

The PerFORM, PET and PLA materials (s. curves 410, 420 and 430) show asignificant increase in the dielectric loss factor with temperature,while the dielectric loss factor of CE 221 and PE materials (s. curves440 and 450) stays nearly constant.

We once again point out that while the dielectric loss factor (orvariations therein) of the material of the mold insert may not directlyinfluence the field distribution (e.g., the local field strength) insidethe molding cavity, it may at least do so indirectly. A change in thedielectric loss factor of the material of the mold insert will generallychange the heat-up the mold insert experiences when permeated by theelectromagnetic field. This local change in temperature in the moldinsert can lead to a corresponding variation of the permittivity of themold insert—which is generally a temperature-dependent quantity, s. FIG.3, for example—which can then influence the electromagnetic field alsooutside of the mold insert.

Another impact a (local or global) variation of the dielectric lossfactor can have on the results of the fusion process, in particular forthe case that the mold insert is arranged directly adjacent to themolding cavity, is the amount of heat-up the mold insert experienceswhen being subjected to the electromagnetic field, in particular theheat-up at the surface of the mold insert which is facing the moldingcavity.

Investigations by the inventors have shown that a certain degree ofheat-up of the material surrounding the molding cavity may be desirablefor the fusion process, and that entirely without ‘pre-heating’ thefusion of the surfaces of the particles of expanded material may beinsufficient.

In some embodiments of the invention, materials with a (local)dielectric loss factor larger than 0.01 and smaller than 0.10, inparticular materials with a (local) dielectric loss factor between 0.01and 0.07, are therefore used in the mold insert. In this regard, the PEmaterial discussed in the context of FIGS. 3 and 4 is less suited thanthe other materials, and the PLA material is also less suited belowtemperatures of roughly 90° C.

Other values are also possible, however, as already mentioned in sectionIII of this document. For example, using polyvinylidene fluoride (PVDF),also called polyvinylidene difluoride, in the construction of the moldinsert, values of 0.2 or even higher can also be realized.

In the following further examples are described to facilitate theunderstanding of the present invention:

1. Mold insert for use in a mold for the manufacture of a cushioningelement for sports apparel, a. wherein the cushioning element ismanufactured from particles of an expanded material, b. wherein anelectromagnetic field is used as an energy carrier to fuse the particlesurfaces, c. wherein the mold insert has been manufactured using anadditive manufacturing method, and d. wherein the mold insert is adaptedto locally adjust the field strength of the electromagnetic field insidea molding cavity of the mold, based at least in part on the geometry ofthe cushioning element.

2. Mold insert according to example 1, wherein the mold insert isadapted to increase the homogeneity of the field strength throughoutmolding cavity during the manufacture of the cushioning element.

3. Mold insert according to example 1 or 2, wherein the local adjustmentof the field strength inside the molding cavity is at least partiallycaused by a local variation in the dielectric properties of the moldinsert.

4. Mold insert according to example 3, wherein the local adjustment ofthe field strength inside the molding cavity is at least partiallycaused by a local variation in the permittivity of the mold insert.

5. Mold insert according to example 4, wherein the local variation inthe permittivity of the mold insert is at least partially caused by alocal variation in the density of the material of the mold insert.

6. Mold insert according to example 5, where a higher density of thematerial of the mold insert results in a higher permittivity of the moldinsert.

7. Mold insert according to example 5 or 6, wherein the local density ofthe material of the mold insert lies between 0.4 g/cm³ and 1.7 g/cm³.

8. Mold insert according to one of examples 3-7, wherein the localadjustment of the field strength inside the molding cavity is at leastpartially caused by a local variation in the dielectric loss factor ofthe mold insert.

9. Mold insert according to example 8, wherein the local dielectric lossfactor of the mold insert lies between 0.01 and 0.10, in particularbetween 0.01 and 0.07.

10. Mold insert according to one of examples 1-9, wherein the moldinsert is arranged adjacent to the molding cavity and influences thegeometry of the molding cavity.

11. Mold insert according to one of examples 8 or 9 in combination withexample 10, wherein the local variation in the dielectric loss factorfurther influences the amount of surface heat-up of the surface of themold insert which is adjacent to the molding cavity during themanufacture of the cushioning element.

12. Mold insert according to one of examples 1-11, wherein the additivemanufacturing method for the mold insert comprises at least one of: 3dprinting; a micro-melt-drop based method; a powder-bed based method;stereolithography, SLA; selective laser sintering, SLS; selective lasermelting, SLM; continuous liquid interface production, CLIP; fuseddeposition modeling, FDM; digital light processing, DLP; multi jetmodeling, MJM; a polyjet method; a film transfer imaging method, FTI;electron beam melting, EBM; electron beam additive manufacturing, EBAM;subtractive rapid prototyping, SRP.

13. Mold insert according to one of examples 1-12, wherein the moldinsert comprises at least one of the following materials: a ceramicfilled resin; a cyanate ester; a polylactic acid/polylactide, PLA; anacrylonitrile butadiene styrene, ABS; polyamide 6/nylon 6, PA6;polyamide 66/nylon 66, PA66; polyamide 12/nylon 12, PA12; a polyetherether ketone, PEEK; a binder system; an epoxy resin; a UV-curingthermoset.

14. Mold insert according to one of examples 1-13, wherein theelectromagnetic field provides the energy to fuse the particle surfacesin form of electromagnetic waves in the radiofrequency part of thespectrum of 30 kHz-300 MHz, or in the microwave part of the spectrum of300 MHz-300 GHz, in particular in the form of electromagnetic waves witha frequency in the range of 25-30 MHz.

15. Mold insert according to one of examples 1-14, wherein thecushioning element is a sole for a shoe, in particular a midsole.

16. Mold for the manufacture of a cushioning element for sports apparelfrom particles of an expanded material, a. wherein an electromagneticfield is used as an energy carrier to fuse the particle surfaces, and b.wherein the mold comprises a mold insert according to one of examples1-15.

17. Mold according to example 16, c. wherein the mold comprises at leasttwo mold parts, d. wherein each of the two mold parts comprises anelectrode used in the provision of the electromagnetic field, e. whereinthe mold insert is placed into one of the two mold parts, f wherein thetwo mold parts may be moved relative to one another in a first directionto open the mold in order to allow loading the mold with the particles,and g. wherein the two mold parts may be moved relative to one anotherin a second direction to close the mold in order to form the moldingcavity between the electrodes.

18. Method for the manufacture of a cushioning element for sportsapparel from particles of an expanded material, a. wherein anelectromagnetic field is used as an energy carrier to fuse the particlesurfaces, and b. wherein the method uses a mold according to examples 16or 17.

19. Cushioning element, in particular, a sole, or a midsole,manufactured with the method according to example 18.

20. Shoe, in particular, a sports shoe, comprising a sole or a midsoleaccording to example 19.

Different arrangements of the components depicted in the drawings ordescribed above, as well as components and steps not shown or describedare possible. Similarly, some features and sub-combinations are usefuland may be employed without reference to other features andsub-combinations. Embodiments of the invention have been described forillustrative and not restrictive purposes, and alternative embodimentswill become apparent to readers of this patent. Accordingly, the presentinvention is not limited to the embodiments described above or depictedin the drawings, and various embodiments and modifications may be madewithout departing from the scope of the claims below.

That which is claimed is:
 1. A mold insert for use in a mold for themanufacture of a cushioning element for sports apparel, a. wherein thecushioning element is manufactured from particles of an expandedmaterial, b. wherein an electromagnetic field is used as an energycarrier to fuse the particle surfaces, c. wherein the mold insert hasbeen manufactured using an additive manufacturing method, and d. whereinthe mold insert is adapted to locally adjust the field strength of theelectromagnetic field inside a molding cavity of the mold, based atleast in part on the geometry of the cushioning element.
 2. The moldinsert according to claim 1, wherein the mold insert is adapted toincrease the homogeneity of the field strength throughout molding cavityduring the manufacture of the cushioning element.
 3. The mold insertaccording to claim 1, wherein the local adjustment of the field strengthinside the molding cavity is at least partially caused by a localvariation in the dielectric properties of the mold insert.
 4. The moldinsert according to claim 3, wherein the local adjustment of the fieldstrength inside the molding cavity is at least partially caused by alocal variation in the permittivity of the mold insert.
 5. The moldinsert according to claim 4, wherein the local variation in thepermittivity of the mold insert is at least partially caused by a localvariation in the density of the material of the mold insert.
 6. The moldinsert according to claim 5, where a higher density of the material ofthe mold insert results in a higher permittivity of the mold insert. 7.The mold insert according to claim 5, wherein the local density of thematerial of the mold insert lies between 0.4 g/cm³ and 1.7 g/cm³.
 8. Themold insert according to claim 3, wherein the local adjustment of thefield strength inside the molding cavity is at least partially caused bya local variation in the dielectric loss factor of the mold insert. 9.The mold insert according to claim 8, wherein the local dielectric lossfactor of the mold insert lies between 0.01 and 0.10, in particularbetween 0.01 and 0.07.
 10. The mold insert according to claim 1, whereinthe mold insert is arranged adjacent to the molding cavity andinfluences the geometry of the molding cavity.
 11. The mold insertaccording to claim 8, wherein the mold insert is arranged adjacent tothe molding cavity and influences the geometry of the molding cavity andwherein the local variation in the dielectric loss factor furtherinfluences the amount of surface heat-up of the surface of the moldinsert which is adjacent to the molding cavity during the manufacture ofthe cushioning element.
 12. The mold insert according to claim 1,wherein the cushioning element is a sole for a shoe, in particular amidsole.
 13. A mold for the manufacture of a cushioning element forsports apparel from particles of an expanded material, a. wherein anelectromagnetic field is used as an energy carrier to fuse the particlesurfaces, and b. wherein the mold comprises a mold insert according toclaim
 1. 14. A method for the manufacture of a cushioning element forsports apparel from particles of an expanded material, a. wherein anelectromagnetic field is used as an energy carrier to fuse the particlesurfaces, and b. wherein the method uses a mold according to claim 13.15. A cushioning element manufactured with the method according to claim14.
 16. The cushioning element of claim 15, wherein the cushioningelement is a sole.
 17. The cushioning element of claim 15, wherein thecushioning element is a midsole.